1. Field of the Invention
The present invention relates to an apparatus for determining the microhardness of thin films or of the surface thin layers of materials.
2. Description of Related Arts
Recently, preparation of thin films has become more and more important in various fields of electronics. In accordance with the development in thin film technology, exact evaluation of the characteristics of thin films has become and important item. Among such characteristics, their hardness or rather their microhardness is very difficult to determine.
For example, VLSI (Very large scaled integrated circuit) is manufactured by forming thin layers of a thickness around 100 nm on a substrate. If the microhardness of the thin layer of VLSI is measured directly, the quality control of the production can be conducted more effectively. Further, measurement of the microhardness of the thin layer of the magnetic disc is earnestly required to improve the abrasive resistance therof with the reading head. For the purpose of determining the microhardness of thin films, several apparatuses have been developed.
One of such apparatuses is described in Bull. Jap. Soc. Prec. Eng., Vol. 3, No. 1, (1968), p. 13. The apparatus illustrated in this article comprises a balance of counterpoised bar type. The poising bar of the balance includes at one end thereof an indenter. The other end of the poising bar is moved upwardly by means of an electromagnet to press the indenter onto a specimen, resulting in an impression on the surface of the specimen. From the value of the applied load by the electromagnet and the area of the impression measured by microscopic observation, the microhardness of the thin film is determined. In this case, observation with eyes is inevitable in determining the microhardness. In addition, the applied load cannot be determined within 0.1 grams precision because of the use of an electromagnet. Therefore, it is difficult to determine the microhardness of a thin film of the order of 0.1 microns with this apparatus.
Another apparatus is shown in Kotai-butsuri (in Japanese), Vol. 8, No. 5, (1973), p. 29-33. With the apparatus illustrated in this article, the microhardness of a specimen is determined by measuring the penetration depth of an indenter into the specimen and the load applied to the indenter for penetrating it into the specimen. With this apparatus, the indenter is driven by means of a stain gauge to penetrate into the surface of the specimen. Thus, the applied load is adjusted by varying the current applied to the strain gauge while observing the current meter of the strain gauge. On the other hand, the penetration depth is measured by means of a capacitor-type displacement measuring device connected to the indenter.
With such a measuring device, it is difficult to detect the contact between the indenter and the specimen without causing an impression to the surface of the specimen. Therefore, the applied load cannot be controlled with high precision and the initial equilibrium state cannot be set up minutely. Furthermore, the penetration depth cannot be determined within 0.01 microns precision, which is not sufficient for the determination of the microhardness of thin films of the order of 0.1 microns. Another disadvantage of the apparatus is that a plurality of measurements must be done by changing the applied load for determining correctly the microhardness of a specimen.
A similar apparatus is described in J. Phys. E: Sci. Instrum. Vol.15, (1982), P. 119-122. In this apparatus, the microhardness of a specimen is also determined by measuring the penetration depth of an indenter into the specimen and the load applied to the indenter for penetrating it into the specimen. The apparatus illustrated in this article comprises an indenter, a capacitor-type displacement measuring device fixed to the indenter, and means for applying a load to the indenter. In this case, however, the indenter is pressed to the specimen by an electrostatic force generated by the load-applying means. The applied load cannot be determined within 1 milligram precision with such load-applying means. In addition, contact between the indenter and the specimen cannot be detected clearly because of the use of a capacitor-type displacement measuring device. Another problem of the apparatus is that electronic charges in the capacitor-type displacement measuring device adversely affect the measurement of the applied load. Furthermore, surrounding conditions should be controlled because the capacitor-type displacement measuring device is sensitive to the moisture in the air. The maintenance of the apparatus accordingly is complicated, which leads to lower reliability.